Motor shaft for rotational-to-direct motion converting motor and method of manufacturing the motor shaft

ABSTRACT

A motor shaft for a rotational-to-direct motion converting motor has a rotation stopping portion formed in a plate shape, and a screw portion formed in a columnar shape. In addition, the motor shaft has a hole, arranged in an end portion of the motor shaft in a longitudinal direction of the motor shaft, for positioning the motor shaft in a form rolling. Therefore, a position shift or a phase shift of thread ridges formed on the screw portion can be prevented.

CROSS-REFERENCE TO THE RELATED APPLICATION

[0001] This application is a continuation of International ApplicationNo. PCT/JP00/02589, whose International filing date is Apr. 20, 2000,the disclosures of which Application are incorporated by referenceherein.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a motor shaft for arotational-to-direct motion converting motor which is, for example, usedfor a valve (EGR-V) of an exhaust gas re-circulation system and has amechanism for converting a rotational motion of a valve motor into areciprocating motion (or a direct driving motion). Also, the presentinvention relates to a method of manufacturing the motor shaft.

[0004] 2. Description of Related Art

[0005] As is disclosed in the Published Unexamined Japanese PatentApplication H7-27023 (1995), an apparatus for controlling an exhaust gasre-circulation control valve (EGR-V) has been known as a prior art. Inthis control apparatus, a rotational motion in a stepping motor (or alinear motor) is converted into a linear motion, the EGR-V is driven, avalve opening is adjusted, and a flow rate of a re-circulated exhaustgas is adjusted. Also, a pushing type control valve, in which a motorshaft pushes a valve shaft to open a valve, and a lifting type controlvalve, in which a motor shaft pulls a valve shaft to open a valve, aredisclosed in the Application.

[0006] Also, in the Published Unexamined Japanese Patent ApplicationH8-49782 (1996), a technique, in which a compression molding isperformed while arranging a non-protruding end of a screw shaft betweenmetal molds, is disclosed as a processing method in the Application.Also, in the disclosure of the Application, the use of anotherprocessing method is allowed on condition that no flash is produced on asurface of an engaging-protruding portion in the processing method.Also, a mechanism, in which a motor shaft and a valve shaft areintegrally formed with each other to fix a valve to an end portion ofthe motor shaft, is disclosed.

[0007] In addition, in the Published Unexamined Japanese PatentApplication H10-215545 (1998), a technique, in which a round bar isformed into a motor shaft by grinding the round bar with a finishingmachine, and a technique, in which a motor shaft is molded according toa metal injection molding method, are disclosed. Also, a technique, inwhich a screw portion is formed according to a form rolling method, arotation regulating portion adapted to a phase (or lead and pitch) ofthe screw portion is formed according to a resin inserting molding or ametal injection molding and the rotation regulating portion and thescrew portion are welded together to form a motor shaft, is disclosed.

[0008] Here, a structure of a general EGR-V is described.

[0009]FIG. 1 is an internal structural diagram of a stepper motordriving type exhaust gas re-circulation control valve which denotes amotor-driven control valve apparatus and in which a stepper motor isused as a motor.

[0010] In FIG. 1, a housing 1 has an input port 2 leading to an exhaustsystem of an engine, an output port 3 leading to an intake system of theengine, a pair of reflux passages 4 a and 4 b, and a water-coolingpassage 14 for cooling the motor and a valve body. A valve seat 6 isinserted into the reflux passage 4 a under pressure, and a roll pin 13prevents the valve seat 6 from coming out from the reflux passage 4 a. 9indicates a bush functioning as a bearing. 8 indicates a holder whichprevents deposits from penetrating into the bush 9. The holder 8 isarranged with the valve seat 6 on the same axis and is placed betweenthe housing 1 and the valve seat 6.

[0011]5 indicates a valve which is arranged to come in contact with thevalve seat 6. The valve 5 is fixed to a valve shaft 7 at caulkingstructure. The valve shaft 7 penetrates through the bush 9, a springholder A10 and a washer 13 are fixed to the valve shaft 7 at caulkingstructure on the opposite side to the valve 5. 12 indicates a spring Awhich is arranged between the spring holder A10 and the housing 1 at acontracted form so as to give a power to the valve 5 in a valve-closedirection.

[0012]20 indicates a stepper motor. An attaching screw 46 attaches thestepper motor 20 to the housing 1 so as to make an axis center of thestepper motor 20 agree with that of the housing 1. 22 indicates a pairof bobbins. A coil 23 is wound on each bobbin 22. A yoke A24 and a yokeB25 functioning as a magnetic path are arranged on the outer peripheryof each bobbin 22. 29 indicates a terminal electrically connected withthe coils 23. A connector is formed of the terminal 29 and a motorhousing 21. 27 indicates a plate A magnetically shielding one coilportion from the other coil portion. 26 indicates a plate B whichprevents resin from flowing into the inner peripheries of the coilportions when the motor housing 21 is formed.

[0013]31 indicates a magnet. 32 indicates a rotor having the magnet 31.A screw portion 32 a and a stopper portion 32 b for stopping themovement of a motor shaft 70 in a longitudinal direction are arranged inthe inner periphery of the rotor 32. The screw portion 32 a is screwedto a screw portion 70 a of the motor shaft 70. 30 indicates a pair ofbearings attached to both ends of the rotor 32. 28 indicates a platespring generating a side pressure given to the bearings 30. 70 indicatesthe motor shaft having the screw portion 70 a. The screw portion 70 a isscrewed to the screw portion 32 a so as to make the motor shaft 70perform a reciprocating motion, so that a rotational motion performed inthe rotor 32 is converted into a linear motion of the motor shaft 70. 34indicates a stopper pin inserted into themotor shaft 70 under pressure.41 indicates amotor bush having a bearing function and a rotationpreventing function for preventing the rotational motion of the motorshaft 70. The rotation preventing function is generated by a hole of themotor bush 41 having a D form at cross section. 40 indicates a motorholder having the same center as that of the motor housing 21. The motorholder 40 is arranged between the motor housing 21 and the housing 1 andholds the bearings 30 and the motor bush 41.

[0014] In the motor having the above configuration, in a valve openingoperation, the rotor 32 including the magnet 31 is rotated in avalve-open direction step by step according to a pulse-shaped voltagesignal which is sent from a control unit (not shown) to the terminal 29.In this case, the number of transmitted pulses agrees with the number ofstepped motions of the rotor 32, so that an open loop control can becorrectly performed. This step-by-step rotation of the rotor 32 istransmitted to the motor shaft 70 through the screw portion 32 a of therotor 32 and the screw portion 70 a of the motor shaft 70. Because arotational motion in the motor shaft 70 is prevented by both a D portion70 b of the motor shaft 70 having a semi-circular shape at cross sectionand a D hole of the bush 41, the rotational motion of the rotor 32 isconverted into a linear motion of the motor shaft 70, and the motorshaft 70 is moved in a valve-open direction (that is, in the lowerdirection in FIG. 1).

[0015] Because a conventional motor shaft for a rotational-to-directmotion converting motor has the above configuration, it is difficult toperform the positioning of the motor shaft 70 in the form rolling, andthere is a case where the screw portion is not correctly positioned.

[0016] Also, a rotation stopping portion (that is, the D portion 70 b)of the motor shaft 70 is made of a material other than that of the motorshaft 70 to adapt the phase of one screw portion 32 a to that of theother screw portion 70 a, and one screw portion 70 a is fixed to therotation stopping portion to make the phase of the screw portion 70 aagree with that of the rotation stopping portion. Therefore, there is aproblem that the number of parts of the motor shaft 70 is increased andthe processing procedure for the motor shaft 70 is complicated.

[0017] In addition, in the manufacturing method of the conventionalmotor shaft 70, because a round bar is formed into the conventionalmotor shaft 70 by grinding the round bar, a portion of the round barremoved in the grinding operation is drawn off as scrap metal.Therefore, there is another problem that an useless portion of the roundbar removed as scrap metal is increased.

[0018] In particular, in cases where the rotation stopping portion ofthe motor shaft 70 is made of the same material as that of the motorshaft 70, it is required to form a round bar having a larger diameterinto a motor shaft. Therefore, an useless portion of the round bar ismoreover increased.

SUMMARY OF THE INVENTION

[0019] The present invention is provided to solve the above problems,and an object of the present invention is to provide a motor shaft for arotational-to-direct motion converting motor in which the positioning ina form rolling operation is easily performed and in which phases ofscrews connected to each other are easily adapted to each other.

[0020] Also, the object of the present invention is to provide a methodof manufacturing the motor shaft in which a material of the motor shaftis efficiently used.

[0021] A manufacturing method of a motor shaft for arotational-to-direct motion converting motor according to the presentinvention comprises a step for forming an end portion of a wire rod intoa large diameter portion, a step for flattening the large diameterportion to form the large diameter portion into a plate portion having aprescribed thickness, a step for taking out a prescribed-shaped rotationstopping portion from the plate portion having the prescribed thickness,and a step for forming thread ridges on the wire rod other than therotation stopping portion. Because the rotation stopping portion isformed after the wire rod is once formed into the large diameterportion, a diameter of the wire rod can be reduced.

[0022] Also, a manufacturing method of a motor shaft for arotational-to-direct motion converting motor according to the presentinvention comprises a step for taking out a prescribed-shaped secondplate material including a rotation stopping portion from a first platematerial, a step for forming the second plate material other than therotation stopping portion into a columnar portion by pressing the secondplate material, and a step for forming thread ridges on the columnarportion. Because the thread ridges is formed after the second platematerial is once formed into the columnar portion, the first platematerial can be thinned.

[0023] Also, the step for forming thread ridges in the manufacturingmethod comprises a step for forming the thread ridges according to aform rolling. Therefore, the thread ridges can be rapidly formed.

[0024] Also, a motor shaft for a rotational-to-direct motion convertingmotor comprises a rotation stopping portion formed in a plate shape, ascrew portion formed in a columnar shape, and a hole, arranged in an endportion of a motor shaft in a longitudinal direction, for positioningthe motor shaft in a form rolling. Therefore, a position shift or aphase shift of the thread ridges formed on the screw portion can beprevented.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025]FIG. 1 is a cross sectional view showing a conventional exhaustgas re-circulation control valve with a rotational-to-direct motionconverting motor.

[0026]FIG. 2 is an exploded view in perspective of a main portion of arotational-to-direct motion converting motor according to a firstembodiment of the present invention;

[0027]FIG. 3A is a front view showing a motor shaft according to thefirst embodiment of the present invention;

[0028]FIG. 3B is a front view showing a motor shaft according to thefirst embodiment of the present invention;

[0029]FIG. 3C is a front view showing a motor shaft according to thefirst embodiment of the present invention;

[0030]FIG. 3D is a front view showing a motor shaft according to thefirst embodiment of the present invention;

[0031]FIG. 3E is a front view showing a motor shaft according to thefirst embodiment of the present invention;

[0032]FIG. 3F is a front view showing a motor shaft according to thefirst embodiment of the present invention;

[0033]FIG. 4A is a front view of the motor shaft shown in FIG. 3B;

[0034]FIG. 4B is a right side view of the motor shaft shown in FIG. 3B;

[0035]FIG. 4C is a plan view of the motor shaft shown in FIG. 3B;

[0036]FIG. 4D is a bottom view of the motor shaft shown in FIG. 3B;

[0037]FIG. 4E is a diagonal view of the motor shaft shown in FIG. 3B;

[0038]FIG. 5A is a front view of the motor shaft shown in FIG. 3A;

[0039]FIG. 5B is a right side view of the motor shaft shown in FIG. 3A;

[0040]FIG. 5C is a plan view of the motor shaft shown in FIG. 3A;

[0041]FIG. 5D is a bottom view of the motor shaft shown in FIG. 3A;

[0042]FIG. 5E is a diagonal view of the motor shaft shown in FIG. 3A;

[0043]FIG. 6A is a front view of the motor shaft shown in FIG. 3C;

[0044]FIG. 6B is a right side view of the motor shaft shown in FIG. 3C;

[0045]FIG. 6C is a plan view of the motor shaft shown in FIG. 3C;

[0046]FIG. 6D is a bottom view of the motor shaft shown in FIG. 3C;

[0047]FIG. 6E is a diagonal view of the motor shaft shown in FIG. 3C;

[0048]FIG. 7A is a front view of the motor shaft shown in FIG. 3D;

[0049]FIG. 7B is a right side view of the motor shaft shown in FIG. 3D;

[0050]FIG. 7C is a plan view of the motor shaft shown in FIG. 3D;

[0051]FIG. 7D is a bottom view of the motor shaft shown in FIG. 3D;

[0052]FIG. 7E is a diagonal view of the motor shaft shown in FIG. 3D;

[0053]FIG. 8A is a front view showing a motor shaft according to thefirst embodiment of the present invention;

[0054]FIG. 8B is a back view of the motor shaft;

[0055]FIG. 8C is a left side view of the motor shaft;

[0056]FIG. 8D is a right side view of the motor shaft;

[0057]FIG. 8E is a plan view of the motor shaft;

[0058]FIG. 8F is a bottom view of the motor shaft;

[0059]FIG. 8G is a diagonal view of the motor shaft;

[0060]FIG. 9(a) to FIG. 9(f) are a plurality of explanatory viewsshowing a series of manufacturing steps of the motor shaft shown in FIG.3B;

[0061]FIG. 10(a) to FIG. 10(e) are a plurality of explanatory viewsshowing another series of manufacturing steps of the motor shaft shownin FIG. 3B;

[0062]FIG. 11A is an explanatory view of a form rolling step performedas one manufacturing step of the motor shaft shown in each of FIG. 3A toFIG. 3E according to the first embodiment of the present invention;

[0063]FIG. 11B is another explanatory view of the form rolling step;

[0064]FIG. 12 is an explanatory view showing a cut-off of a material ofeach motor shaft from a plate material according to the first embodimentof the present invention; and

[0065]FIG. 13 is other front, plan, bottom and side views of the motorshaft shown in FIG. 3B.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0066] The invention will now be described with reference to theaccompanying drawings.

[0067] Embodiment 1

[0068]FIG. 2 is an exploded view in perspective of a main portion of arotational-to-direct motion converting motor according to a firstembodiment of the present invention.

[0069] In FIG. 2, 50 and 51 respectively indicate a stator formed of aniron core. A coil is wounded on each of the stators 50 and 51. 31indicates a magnet formed of a permanent magnet. 32 indicates a rotorrotating according to a rotational power which is generated in themagnet 31 by magnetic field generated by supplying electric current tothe stators 50 and 51. 32 b indicates a stopper portion which is formedon an end side of the rotor 32 facing a valve shaft and functions as astopper on the motor side of a motor shaft 33 (described later). 33indicates the motor shaft comprising a screw portion 33 a, aplate-shaped rotation regulating portion 33 b and a pushing-out area 33d. The screw portion 33 a is screwed to the rotor 32. The rotationregulating portion 33 b regulates a rotational motion around an axis ofthe motor shaft 33. The pushing-out area 33 d is arranged on one end ofthe motor shaft 33 in a longitudinal direction of the motor shaft 33.Also, a contact portion 33c is formed on a screw portion side of therotation regulating portion 33 b. The contact portion 33 c is in contactwith the stopper portion 32 b of the rotor 32 to limit a motion of themotor shaft 33 in the longitudinal direction. The other configuration ofa rotational-to-direct motion converting motor is the same as that shownin FIG. 1, so that the other configuration is not shown in FIG. 2.

[0070] In a phase matching (or a rotational direction matching) in theparts of the rotational-to-direct motion converting motor, a positionalrelationship of the stators 50 and 51 (pawl portions of the stators 50and 51 are only displayed in FIG. 2) is determined by inserting convexportions arranged in the outer peripheries of the stators 50 and 51 intoconcave portions arranged in the outer peripheries of the stators 50 and51 so as to make the phase of the stator 50 match with that of thestator 51. Also, in the forming of the motor housing 21, convex portionsof a metal mold of the motor housing 21 and concave portions (or holes)of the stators 50 and 51 are placed to maintain the phases of thestators 50 and 51, so that the phases of the stators 50 and 51 matchwith each other. Thereafter, the motor housing 21 and the motor holder40 are fixed to each other according to a convex-concave structure inthe same manner. In addition, a positional relationship of the motorholder 40 and the motor bush 41 is determined according to anrectangular outer shape of the motor bush 41. In contrast, a phase ofthe rotor 32 and a phase of the magnet 31 are determined according to aconvex-concave structure of both the rotor 32 and the magnet 31. Thatis, a phase of magnetic poles of the magnet 31 and a phase of thestopper portion 32 b are determined, and a phase of the screw portion 32a is determined.

[0071] In addition, phases of function portions of the motor shaft 33are determined. In detail, the motor shaft 33 structurally has the screwportion 33 a and the plate-shaped rotation regulating portion 33 barranged on the motor output side, the flat-shaped contact portion 33 c,which is in contact with the stopper portion 32 b of the rotor 32, isformed on an end surface of the rotation regulating portion 33 b placedon the screw portion side, and the motor shaft 33 has the pushing-outarea 33 d which is placed in the opposite direction to the screw portion33 a and is in contact with the valve shaft 7.

[0072] In this embodiment, the structure of the pushing-out area 33 d ofthe motor shaft 33 has a flat shape having no concave or convex portion.However, it is applicable that the pushing-out area 33 d have one ofstructures shown in FIG. 3A to FIG. 3F.

[0073] In FIG. 3A to FIG. 3F, the pushing-out area 33 d formed in a flatshape is shown in FIG. 3A and FIG. 5A to FIG. 5E. The motor shaft 33having the flat-shaped pushing-out area 33 d can be easily formedaccording to a punching processing, so that the manufacturing of themotor shaft 33 can be easily performed.

[0074] Next, in FIG. 3B, FIG. 4A to FIG. 4E and FIG. 13, a protrudingportion 33 e is formed in an axial central area of themotor shaft 33,and the end surfaceof theprotruding portion 33 e functions as thepushing-out area 33 d. This type of motor shaft 33 can be easily formedaccording to the punching processing, so that the manufacturing of themotor shaft 33 can be easily performed. Also, an area of the pushing-outarea 33 d coming in contact with the valve shaft 7 can be reduced, and aspace adjacent to a contacting area of the motor shaft 33 with the valveshaft 7 can be reduced.

[0075] Also, in FIG. 3C and FIG. 6A to FIG. 6E, two protruding portions33 e are formed symmetrically with respect to the axis of the motorshaft 33, and the end surfaces of the protruding portions 33 e functionas the pushing-out area 33 d. This type of motor shaft 33 can be easilyformed according to the punching processing, so that the manufacturingof themotor shaft 33 can be easily performed. Also, an area of thepushing-out area 33 d can be widened while manufacturing the lightweightmotor shaft 33.

[0076] Here, in FIG. 3A to FIG. 3C, the motor shaft 33 used for apushing-out type EGR-V, in which the valve 5 goes away from the valveseat 6 (that is, the valve 5 is opened) when the valve shaft 7 is pushedby the motor shaft 33, is shown. However, as a motor shaft 33 used for atype of EGR-V other than the pushing-out type EGR-V, a motor shaft 33used for a lifting type EGR-V, in which the valve 5 goes away from thevalve seat 6 when the valve shaft 7 is lifted by the motor shaft 33, isstructurally described hereinafter.

[0077] In FIG. 3D and FIG. 7A to FIG. 7E, the motor shaft 33 has aT-shaped rotation regulating portion 33 b, two lifting areas 33 f of twoprotruding portions 33 e are engaged with the valve shaft 7, and thevalve shaft 7 is lifted by the motor shaft 33. This type of rotationregulating portion 33 b can be easily formed according to the punchingprocessing, so that the manufacturing of the motor shaft 33 can beeasily performed.

[0078] Also, in FIG. 3E, a hole 33 g is formed in the central area ofthe rotation regulating portion 33 b, a lifting area 33 f of the hole 33a is engaged with the valve shaft 7, and the valve shaft 7 is lifted bythe motor shaft 33. This type of motor shaft 33 can be easily formedaccording to the punching processing, so that the manufacturing of themotor shaft 33 can be easily performed. Also, no protruding portion isarranged in the motor shaft 33, but the hole 33 a is formed in the motorshaft 33. Therefore, a size of the motor shaft 33 can be reduced.

[0079] Also, in FIG. 8A to FIG. 8G, the end portion of the motor shaft33 is bent in a radial direction (in this embodiment, the end portion isdivided into three end portions, and each end portion is bent) of themotor shaft 33, so that three protruding portions 33 e are formed. Endsurfaces of the three protruding portions 33 e function as three liftingareas 33 f. Also, in cases where a hole is formed in the motor bush 41so as to make the screw portion 33 a of the motor shaft 33 pass throughthe hole, the parts can be easily assembled into therotational-to-direct motion converting motor. This type of motor shaft33 can be easily formed according to the punching processing and abending processing, so that the manufacturing of the motor shaft 33 canbe easily performed. Also, because the protruding portions 33 e areformed on the flat surface side of the plate-shaped rotation regulatingportion 33 b, the shape of the motor shaft 33 is similar to a columnarshape. Therefore, the arrangement of the columnar-shaped rotor 32, thevalve shaft 7 and the motor shaft 33 can be efficiently and easilydetermined. Also, the protruding portions 33 e bent in the radialdirection function so as to prevent themotor shaft 33 fromcomingofffromthemotor bush 41.

[0080] In addition, the motor shaft 33 shown in FIG. 8A to FIG. 8G canbe used for the pushing-out type EGR-V. In this case, a contactingsurface of the motor shaft 33 with the valve shaft 7 can be widened, themotor shaft 33 reliably comes in contact with the valve shaft 7 and canpush the valve shaft 7.

[0081] Because the structure and function of the motor shaft 33 otherthan those of the motor shaft 33 used for the lifting type EGR-V aredescribed in the Published Unexamined Japanese Patent ApplicationH7-23323 (1995), a detailed description of the other structure andfunction of the motor shaft 33 is omitted. In brief, in the lifting typeEGR-V, the valve shaft 7 is moved to the valve seat 6, the valve shaft 7comes in contact with the valve seat 6, and the EGR-V is closed. Incontrast, the valve shaft 7 is moved in a direction of the motor 20, thevalve shaft 7 goes away from the valve seat 6, and the EGR-V is opened.To design the EGR-V so as to make the EGR-V be closed in the failure ofthe EGR-V, a spring is arranged to give a power to the valve shaft 7 soas to move the valve shaft 7 in a valve-close direction. Therefore, whenthe EGR-V is opened, it is required to make the motor shaft 33 lift thevalve shaft 7 in a direction of the motor 20.

[0082] Also, as shown in FIG. 3F, the motor shaft 33 shown in FIG. 3D isused for the pushing-out type EGR-V. In this case, the motor shaft 33 isnormally moved in the valve-close direction to push the valve shaft 7,so that the EGR-V is opened. Also, the motor shaft 33 is moved in thevalve-open direction to close the EGR-V by using a spring power of avalve shaft spring 50. In cases where the closing of the EGR-V cannot besufficiently performed, it is possible to design the motor shaft 33 soas to make the lifting area 33 f forcibly lift the valve shaft 7, sothat the EGR-V can be reliably set in a valve-close condition.

[0083] Therefore, in cases where the EGR-V cannot be closed by only thespring power of the valve shaft spring 50 because of the distortion ofthe valve shaft 7 or the like, a motor driving power given by the motorshaft 33 is added to the valve shaft 7, and the EGR-V can be forciblyclosed. Therefore, the EGR-V excellent in fail safe can be obtained.

[0084] Here, in cases where a pushing-out area is arranged in the motorshaft 33, the lifting type EGR-V can be forcibly closed by the motorshaft 33 in the same manner as the pushing-out type EGR-V.

[0085]FIG. 9(a) to FIG. 9(f) are a plurality of explanatory viewsshowing a series of manufacturing steps of the motor shaft shown in FIG.3B.

[0086] In a step shown in FIG. 9(a), a wire rod, which has almost thesame diameter as that of the screw portion 33 a of the motor shaft 33,is initially prepared.

[0087] In a step shown in FIG. 9(b), the wire rod is cut to obtain ametal rod which has a length required to manufacture the motor shaft 33.In this case, a center hole 33 h required for a form rolling operationis formed on an end surface of the metal rod placed on the side of thescrew portion 33 a. Also, a portion of the metal rod placed on the sideof the rotation regulating portion 33 b is pressed in a radial directionof the metal rod to form a large diameter portion. (header processing)

[0088] In a step shown in FIG. 9(c), the large diameter portion formedin the step shown in FIG. 9 (b) is pressed in the radial direction byusing an oil hydraulic pressing machine, so that the large diameterportion is flattened to the same thickness as that of the rotationregulating portion 33 b. (flattening processing)

[0089] In a step shown in FIG. 9(d), a pattern-draw-molding is performedfor the flattened portion obtained in the step shown in FIG. 9(c) byusing the oil hydraulic pressing machine to form the rotation regulatingportion 33 b.

[0090] In a step shown in FIG. 9(e), a center hole 33 h required for theform rolling operation is formed on the end surface of the rotationregulating portion 33 b.

[0091] In a step shown in FIG. 9(f), the form rolling operationdescribed later in detail is performed to roughly form the motor shaft33, a barrel polishing is performed for the motor shaft 33 to removeflash from the motor shaft 33, and the motor shaft 33 is formed.

[0092]FIG. 10(a) to FIG. 10(e) are a plurality of explanatory viewsshowing another series of manufacturing steps of the motor shaftdifferent from that shown in FIG. 9(a) to FIG. 9(f).

[0093] In a step shown in FIG. 10(a), a metal plate material, which hasthe same thickness as that of the rotation regulating portion 33 b, isprepared.

[0094] In a step shown in FIG. 10(b), an outlined motor shaft is takenout from the metal plate by using a power pressing machine. In thiscase, a portion of the outlined motor shaft corresponding to therotation regulating portion 33 b has the same shape as that of therotation regulating portion 33 b, and the other portion of the outlinedmotor shaft corresponding to the screw portion 33 a has an excessivewidth required for a rolling step performed later.

[0095] Also, as shown in FIG. 12, in cases where a plurality of outlinedmotor shafts are taken out from the metal plate material while reducinga non-use portion of the metal plate material, the metal plate materialcan be effectively used.

[0096] In a step shown in FIG. 10(c), a rolling processing is performedfor the other portion of the outlined motor shaft corresponding to thescrew portion 33 a while placing the other portion of the outlined motorshaft between metal molds, and the other portion of the outlined motorshaft is processed to have a columnar shape. In cases where the otherportion of the outlined motor shaft cannot be precisely formed into acolumnar-shaped bar by performing the rolling processing only once, itis applicable that the rolling processing be repeatedly performed.

[0097] In a step shown in FIG. 10(d), a pair of center holes 33 h areformed on both ends of the outlined motor shaft according to ahole-making processing orapress processing to perform a form rollingprocessing described later for the outlined motor shaft.

[0098] In a step shown in FIG. 10(e), the form rollingprocessingdescribed later in detail is performed for the outlined motor shaft toroughly form the motor shaft 33, a barrel polishing is performed for themotor shaft 33 to remove flash from the motor shaft 33, and the motorshaft 33 is formed.

[0099]FIG. 11A and FIG. 11B are a plurality of explanatory views showingthe form rolling processing.

[0100] In FIG. 11A and FIG. 11B, 10a and 100 b indicate a pair of formrolling plates. A plurality of oblique grooves are formed on a surfaceof each form rolling plate 100 a or 10 b. The screw portion 33 a of themotor shaft 33 is placed between the form rolling plates 10 a and 100 bunder pressure, the form rolling plates 100 a and 100 b are moved up anddown in the opposite direction to each other, and thread ridges areformed in the screw portion 33 a.

[0101] Here, before the thread ridges are formed by using the formrolling plates 100 a and 100 b, the rotation regulating portion 33 b isfixed by a positioning tool 101 to perform the positioning of the motorshaft 33 in an axis-around direction (that is, a rotational direction),and two center supports 102 are inserted into the center holes 33 h toperform the positioning of the motor shaft 33 in a longitudinaldirection of the motor shaft 33.

[0102] Next, the procedure of the form rolling operation is described.

[0103] The center supports 102 are inserted into the center holes 33 hin the longitudinal direction to fix the motor shaft 33, the motor shaft33 is pressed by the positioning tool 101 in the upper direction, andthe positioning of the motor shaft 33 is performed.

[0104] Thereafter, the motor shaft 33 is moved toward the form rollingplates 100 a and 100 b, and the positioning tool 101 is moved in thelower direction before the forming of the thread ridges. Therefore, themotor shaft 33 can be rotated.

[0105] Thereafter, thescrew portion 33 a is rotated while being pressedby the form rolling plates 100 a and 100 b and while being positioned bythe center supports 102 in the longitudinal direction, and threadridges, of which a rotational phase is uniform, are formed on the screwportion 33 a.

[0106] As is described above, in the present invention, a manufacturingmethod of a motor shaft for a rotational-to-direct motion convertingmotor comprises a step for forming an end portion of a wire rod into alarge diameter portion, a step for flattening the large diameter portionto form the large diameter portion into a plate portion having aprescribed thickness, a step for taking out a prescribed-shaped rotationstopping portion from the plate portion having the prescribed thickness,and a step for forming thread ridges on the wire rod other than therotation stopping portion. Because the wire rod is formed into therotation stopping portion after the wire rod is once formed into thelarge diameter portion, a diameter of the wire rod can be reduced.

[0107] Also, a manufacturing method of a motor shaft for arotational-to-direct motion converting motor comprises a step for takingout a prescribed-shaped second plate material including a rotationstopping portion from a first plate material, a step for forming thesecond plate material other than the rotation stopping portion into acolumnar portion by pressing the second plate material, and a step forforming thread ridges on the columnar portion. Because the formation ofthe thread ridges is performed after the second plate material is formedinto the columnar portion, the first plate material can be thinned.

[0108] Also, the step for forming thread ridges in the manufacturingmethod comprises a step for forming the thread ridges according to aform rolling. Therefore, the thread ridges can be rapidly formed.

[0109] Also, a motor shaft for a rotational-to-direct motion convertingmotor comprises a rotation stopping portion formed in a plate shape, ascrew portion formed in a columnar shape, and a hole, arranged in an endportion of a motor shaft in a longitudinal direction, for positioningthe motor shaft in a form rolling. Therefore, a position shift or aphase shift of the thread ridges formed on the screw portion can beprevented.

[0110] As is described above, a motor shaft for a rotational-to-directmotion converting motor and a method of manufacturing the motor shaftaccording to the present invention are used for a valve (EGR-V) of anexhaust gas re-circulation system and are appropriate to the conversionof a rotational motion of a valve motor into a reciprocating motion (ora direct driving motion).

[0111] Also, the motor shaft for a rotational-to-direct motionconverting motor and the method of manufacturing the motor shaft areappropriate to the manufacturing of a rotational-to-direct motionconverting motor in which a mechanism for converting a rotational motionof a valve motor into a reciprocating motion (or a direct drivingmotion) is arranged.

What is claimed is:
 1. A method of manufacturing a motor shaft for arotational-to-direct motion converting motor comprising: a step forforming an end portion of a wire rod into a large diameter portion; astep for flattening the large diameter portion to form the largediameter portion into a plate portion having a prescribed thickness; astep for taking out a prescribed-shaped rotation stopping portion fromthe plate portion having the prescribed thickness; and a step forforming thread ridges on the wire rod other than the rotation stoppingportion.
 2. A method of manufacturing a motor shaft for arotational-to-direct motion converting motor comprising: a step fortaking out a prescribed-shaped second plate material including arotation stopping portion from a first plate material; a step forforming the second plate material other than the rotation stoppingportion into a columnar portion by pressing the second plate material;and a step for forming thread ridges on the columnar portion.
 3. Amethod of manufacturing a motor shaft for a rotational-to-direct motionconverting motor according to claim 1 , wherein the step for formingthread ridges comprises a step for forming the thread ridges accordingto a form rolling.
 4. A method of manufacturing a motor shaft for arotational-to-direct motion converting motor according to claim 2 ,wherein the step for forming thread ridges comprises a step for formingthe thread ridges according to a form rolling.
 5. A motor shaft for arotational-to-direct motion converting motor comprising: a rotationstopping portion formed in a plate shape; a screw portion formed in acolumnar shape; and a hole, arranged in an end portion of a motor shaftin a longitudinal direction, for positioning the motor shaft in a formrolling.